Answer:
The answer to the question provided is 

Step-by-step explanation:
T
 
        
             
        
        
        
2+x=2x-15
>> 2+15=2x-x
>> 17 = x
So the answer is <u>17</u>
        
                    
             
        
        
        
The tangent line is perpendicular to the radius from the center of the circle to the point of tangency. 
ΔDCE is similar to ΔDBA
DC/DB=DE/DA
15/50=DE/40
DE=12